Process for preparing 9-(2-hydroxyethoxymethyl)-guanine

ABSTRACT

There is disclosed a process for preparing 9-(2-hydroxyethoxymethyl)-guanine (acyclovir) of the formula IV ##STR1## wherein a novel compound of the formula I ##STR2## wherein R and R&#39; may be the same or different and represent hydrogen, (C 1  -C 8 )acyl or benzyl and R 1  represents (C 1  -C 8 )acyl, is hydrolyzed basic conditions. Also disclosed is the novel compound of the formula I, a process for the preparation thereof by condensing a novel compound of the formula II ##STR3## with a compound A--CH 2  --O--CH 2  CH 2  --OR&#39; (A is a leaving group, Q is hydrogen or a leaving group), the novel compound of the formula II and a process for the preparation thereof by means of condensing glyoxal hydrate and a compound of the formula V ##STR4##

This is a continuation-in-part of U.S. Ser. No. 807,724 filed Dec. 11, 1985 now U.S. Pat. No. 4,701,526 is incorporated by reference herein.

The present invention relates to a process for preparing 9-(2-hydroxyethoxymethyl)-guanine (acyclovir) of the formula IV ##STR5## via novel N²,1-substituted purins of the general formula ##STR6## wherein R and R' may be the same or different and represent hydrogen, (C₁ --C₈)acyl or benzyl and R₁ represents (C₁ --C₈)acyl, to these novel intermediates of the formula I, to a process for preparing intermediates of the formula I, to novel intermediates of the formula II hereinafter and to a process for the preparation thereof.

Acyclovir is a well-known agent for therapy of virus infections (Zovirax) (Schafer H. J., Beauchamp L. M., de Miranda P., Elion G. B., Bauer D. J., and Collins P. (1978) Nature (London) 272 583-585).

R is preferably acetyl group and isobutyryl group and R₁ is preferably acetyl group.

The compound of the formula IV is prepared according to the inventive process in such a way that a compound of the general formula I ##STR7## is converted, i.e. hydrolyzed, into the compound IV under basic conditions, e.g. in mild basic conditions such as 50% aqueous methyl amine or in strong basic medium such as about 1M NaOH at room temperature or under slight heating. The use of strong basic medium provides for a very smooth and simple reaction route, along with a very satisfactory yield.

The compounds of formula I are novel compounds and represent another object of the invention.

They are prepared by a process, which is also an object of the present invention, in such a way that a compound of the general formula II ##STR8## is condensed with a compound of the formula III

    A--CH.sub.2 --O--CH.sub.2 --CH.sub.2 --OR'

wherein A represents a leaving group and Q represents a hydrogen atom or a leaving group, whereas R, R' and R₁ have the above meanings.

The leaving groups A and Q may be e.g. acetoxy or halo group.

As reaction mediums toluene and related aromatic solvents or dichloromethane and related halogenated hydrocarbons are used. The process may be carried out at 110° C. in toluene with A═CH₃ COO as leaving group and at room temperature with A═halo group in dichloroethane, resp. As catalysts e.g. p-toluenesulfonic acid, AlCl₃, SnCl₄, HgBr₂ are used.

The compounds of the formula II are novel compounds and represent a further object of the invention. The process for the preparation thereof is also a novel process.

Thus, a further object of the invention is a process for preparing compounds of the general formula II, which is characterized in that a N² -substituted guanine derivative of the formula V ##STR9## is condensed with glyoxal hydrate into a compound of the formula II ##STR10## wherein R and Q represent hydrogen atoms and R₁ has the above meanings.

The compound of the formula II is thus prepared from N²,9-diacetylguanine (Hrebanecky H., Farkas J. in: NUCLEIC ACID CHEMISTRY, Part I, p. 13; L. B. Townsend, R. Stuart Tipson Ed.) and glyoxal monohydrate in dry pyridine at room temperature. The reaction is usually carried out in the ratio 3.5-8.0 mole glyoxal per 1 mole N²,9-diacetylguanine. The obtained intermediate II (R=H) is further acetylated with an appropriate anhydride in pyridine to intermediate II (R is preferably acetyl or isobutyryl) and the latter is condensed with the compound of the formula III (A is preferably --CH₃ COO) in toluene at reflux temperature and in the presence of catalytic amounts of an acid (preferably p-toluenesulfonic acid). The reaction is generally carried out with an excess of the reactant III (1.2 mole) over the compound II (1 mole).

The starting compounds for preparing novel compounds according to the invention are idsclosed in patent as well as in scientific literature. By preparing compounds of the formula I according to the present invention, there have increased the solubility and the reactivity of the starting raw material for the preparation of acyclovir (N²,9-ciacetyl-guanine) in aromatic solvents and especially in halogenated aliphatic solvents. The selectivity for condensation with the compounds of the general formula II has increased, too, preferably in the 9-position, whereby the total reaction yields have increased.

The processes are illustrated by the following non-limiting Examples.

Example 1

N²,9(7)-diacetyl guanine

Guanine (152 g) is suspended in N-methyl-2-pyrrolidone (800 ml) and acetic anhydride (250 ml). The reaction mixture is heated to 150° C. and stirred for 2 to 3 hours so that all guanine is dissolved. The solution is cooled to room temperature and left in refrigerator overnight. Crystals are sucked off, suspended in ethyl acetate (500 ml), repeatedly sucked off and washed with fresh ethyl acetate (50 ml). The product is dried in a drier at 50° C. to a constant weight. The yield is 200 g of N² -9(7)-diacetyl guanine (85%). The reaction mixture liquor is returned to the reaction vessel, guanine (100 g) and acetic anhydride (150 ml) are added thereto and the process is repeated. There are obtained further 150 g of N²,9(7)-diacetyl guanine. The total yield is 96%.

Example 2

Glyoxal-N² -acetyl guanine adduct

Glyoxal monohydrate (280 g) is suspended in dry pyridine (950 ml) and the reaction mixture is stirred for 1 hour at 50° C., whereby all glyoxal is dissolved. To this solution N²,9(7)-diacetyl guanine (236 g) is added and the reaction mixture is stirred vigorously for 1.5 hours. Pyridine is evaporated at 50° C. and reduced pressure (67 mbar); water (1000 ml) is added to the residue and the stirring is continued for half an hour, whereat the solid residue is dissolved. The azeotrope (pyridine-water) (400 ml) is distilled off at 50° C. under reduced pressure. A white precipitate begins to form already during evaporation. The residue in the flask is poured into cold water (2500 ml), stirred for about 1 hour and left in a refrigerator overnight. The precipitate is sucked off, washed with water (150 ml) and dried in a drier. Yield: 227 g of the adduct of the formula II (R=hydrogen, R₁ ═CH₃ CO) (90%), m.p 223° C.

Analysis for C₉ H₉ N₅ O₄ ; m/e=251

¹ H NMR--DMSO--d₆ δ_(DSS) : 2.68 (s, 3, CH₃ CO); 5.55 (dd, 2, CH); 8.10 (s, 1, H₈)

Example 3

Tetraacetyl-glyoxal-gyanine adduct

Adduct II (252 g) (R═H) is dissolved in pyridine (2500 ml). Acetic anhydride (280 ml) is poured into the solution and the stirring is continued for 1.5 hours at room temperature. Pyridine is evaporated at 50° C. under reduced pressure. Ethyl acetate (1000 ml) is poured to the residue, the mixture is stirred for 1 hour at room temperature and left in a refrigerator overnight. White crystals are sucked off, washed with ethyl acetate (150 ml) and dried in a drier to a constant weight. There are obtained 272 g of product II (R═CH₃ CO, Q═CH₃ CO) (72%). Ethyl acetate is washed three times with a 5% NaHCO₃ solution and finally with water, dried with Na₂ SO₄ and at evaporation to dryness, there are obtained additional 72 g of the product. The total yield is 93%, m.p. 197°-199° C. from ethyl acetate.

Analysis for C₁₅ H₁₅ N₅ O₇ ; m/e=377

¹ H NMR CDCl₃ δ_(TMS) : 2.1 (ds, 6 Ac), 2.7 (s, 3, NAc); 2.83 (s, 3, NAc); 6.8 (broad, 2, CH); 8.35 (s, 1 H₈)

Example 4

Diacetoxy-glyoxal-N² -acetylguanine adduct

Method A

Adduct II (252 g) (R═H, Q═H) is dissolved in pyridine (2500 ml) and acetic anhydride (280 ml). The mixture is stirred for 1.5 hours at room temperature, pyridine is evaporated at 50° C. under reduced pressure; to the residue there is added 50% ethyl alcohol (800 ml) and the mixture is heated to reflux temperature. Heating at reflux is continued for 15 minutes until a clear solution is obtained, the contents of the flask are slowly cooled to room temperature and left in a refrigerator overnight. The precipitated crystals are sucked off, washed with 50% ethyl alcohol and dried in a drier. Yield: 234 g (70%), m.p. 242°-243° C.

Analysis for C₁₃ H₁₃ N₅ O₆ ; m/e=335

¹ H NMR CDCl₃ δ_(TMS) : 2.15 (s, 6, Ac); 2.83 (s, 3, NAc); 6.82; 6.93 (dd, 2, CH); 8.15 (s, 1, H₈)

Method B

Compound II (272 g) (R═Ac, Q═Ac) is suspended in 50% ethyl alcohol (1200 ml), the suspension is heated at reflux for 15 minutes or for such a period that all solid is dissolved. The contents are slowly cooled to room temperature and put into a refrigerator overnight. Crystals are sucked off, washed with 50% ethyl alcohol and dried. There are obtained 173 g (72%) of the product II (R═Ac, Q═H).

Example 5 Method A

9-(2-acetoxyethoxymehyl)-diacetoxy-glyoxal-N² -acetyl guanine adduct (R═CH₃ CO, R₁ ═CH₃ CO)

Compound II (3.35 g) (R═CH₃ CO, R₁ ═CH₃ CO, Q═H) and 2-oxo-1,4-butan-dioldiacetat III (2 g; R═CH₃ CO) (Senkus M., J. Amer. Chem. Soc. 68 734 (1946)) and p-toluene sulfonic acid (0.03 g) in dry toluene (40 ml) are stirred for 7 hours at reflux. Toluene is evaporated to dryness, benzene (150 ml) is added, the suspension is heated to ebullition under stirring and is hot filtered over a glass filter. On the filter there remain 2 g (44%) of compound I (R═CH₃ CO, R₁ ═CH₃ CO), which is crystallized from toluene, m.p. 197°-199° C.

Analysis for C₁₈ H₂₁ N₅ O₉ ; m/e=451

¹ H NMR CDCl₃ δ_(TMS) : 2.05 (s, 3, Ac); 2.12 (s, 3, Ac); 2.35 (s, 3, Ac); 2.75 (s, 3, NAc); 3.69 (m, 2, CH₂ O); 3.74 (m, 2, CH₂ O); 5.5 (s, 2, NCH₂); 6.87 (dd, 2, CH); 7.84 (s, 1, H₈)

Example 6 Method B

Diisobutyroxy-glyoxal-N² -acetyl guanine adduct II (R═--COCH(CH₃)₂, R₁ ═CH₃ CO, Q═H)

Compound II (1.26 g) (R═H, R₁ ═CH₃ CO, Q═H) is suspended in dry pyridine (25 ml), isobutyric anhydride (2.5 ml) is added and the mixture is stirred overnight. Pyridine is evaporated, the residue is dissolved in ethyl acetate and the solution is washed with water (40 ml), a 5% NaHCO₃ solution (3×20 ml) and finally with water (20 ml). The solution is dried over Na₂ SO₄ and there are obtained 1.55 g of a crude product. 50% ethyl alcohol (50 ml) is added and it is heated at reflux for 15 minutes. The solution is evaporated and there is added a small amount of ethyl acetate. There are obtained 1.2 g of the product with m.p. 171°-172° C.

Analysis for C₁₇ H₂₁ N₅ O₆ ; m/e=391

¹ H NMR CDCl₃ δ_(TMS) : 1.16 (s, 3, CH(CH₃)₂); 1.25 (s, 3, CH)CH₃)₂); 2.53 (m, 2, CH(CH₃)₂); 2.8 (s, 3, NAc); 6.7 (dd, 2, CH); 8.15 (s, 1, H₈)

Example 7

9-(2-acetoxyethoxymethyl)-diisobutyroxyglyoxal-N² -acetylguanine adduct

Compound II (200 mg) (R═COCH(CH₃)₂, R₁ ═CH₃ CO, Q═H, R'═CH₃ CO) is heated at reflux for 5 minutes in hexametyhldisilazane in the presence of a catalytic amount of ammonium sulfate. Within said period all starting material is dissolved and there is obtained a silylated product II (R═COCH(CH₃)₂, R₁ ═CH₃ CO, Q═Si(CH₃)₃), which is, immediately after evaporating the excess of the solvent, dissolved in dry benzene (15 ml) and there are added HgBr₂ (180 mg) and BrCH₂ OCH₂ CH₂ OAc (100 mg) Robins M. J., Hatfield P. W., Canad. J. Chem. (1981) 60 547-553). The mixture is heated at reflux overnight, the solvent is evaporated and the residue is dissolved in chloroform. The solution is washed with a 20% KJ solution (2×10 ml) and water (2×10 ml), dried over Na₂ SO₄ and evaporated to foam. Yield: 210 mg of the crude product. After chromatography on 10 g of silicagel, there is obtained the compound I (R═--COCH(CH₃)₂, R₁ ═CH₃ CO, R'═CH₃ CO) (120 g).

¹ H NMR CDCl₃ δ_(TMS) : 1.11 (s, 6, CH(CH₃)₂); 1.25 (s, 6, CH(CH₃)₂ ; 2.06 (s, 3, Ac); 2.8 (s, 3, NAc); 3.7 (m, 2, OCH₂); 3.76 (m, 2, OCH₂); 5.5 (s, 2, NCH₂ O); 6.85 (dd, 2, CH); 7.80 (s, 1 H₈)

Example 8

9-(2-hydroxyethoxymethyl)-guanine (acyclovir)

Compound I (1 g) (R═CH₃ CO, R₁ ═CH₃ CO) is put into 50% methylamine (10 ml). The reaction mixture is cleared at once in exothermic reaction, heated for further 15 minutes on a steam bath or left overnight at room temperature. The solvent and excessive amine are evaporated under reduced pressure, ethyl alcohol (10 ml) is added and the solvent is evaporated once more. Methyl alcohol (15 ml) is added to the residue, methyl alcohol is decanted and the residue is crystallized from a methyl alcohol/water mixture to obtain product IV (400 mg; 81%), m.p. 264°-266° C., m/e 225.

¹ H NMR DMSOd₆ δ_(DSS) : 3.49 (m, 4, OCH₂); 4.69 (s, 1, OH); 5.4 (s, 2, NCH₂ O); 6.54 (s, 2, NH₂); 7.84 (s, 1, H₈)

Example 9

NaOH (3 g, 0.075 mole) is dissolved in water. 9-(2-acetoxyethoxymethyl)diacetylglyoxal-N² -acetylguanine adduct (4.51 g; 0.01 mole) is added at room temperature whilst stirring. After 10 minutes reaction mixture is cleared; the temperature rises to 30° C. Stirring is continued for another 5 hours at temperature 25°-30° C. Then the reaction mixture is cooled to 5°-10° C.and pH is adjusted to 7 in a course of 10 minutes with 10% HCl. It is stirred for another two hours, filtrated by suction and washed with fresh water. The cake is returned into the flask, water (60 ml) is added, active carbon (0.2 g) is added, too, heated to boiling point and stirred for 15 minutes. The solution is then hot filtered by suction over dicalite. From the filtrate a white precipitate is being formed during filtering by suction. The filtrate is put into refrigerator over night, then the precipitate is filtered by suction, washed with fresh water (10 ml), acetone (10 ml) and dried in an air drier at temperature 50° C. Acyclovir (1.46 g; 65%) is obtained. 

We claim:
 1. Process for preparing 9-(2-hydroethyoxymethyl)-guanine of the formula ##STR11## characterized in that a compound of the formula I ##STR12## wherein R and R' may be the same or different and represent hydrogen, (C₁ --C₈)acyl or benzyl and R₁ represents (C₁ --C₈)acyl is hydrolysed under basic conditions.
 2. The method of claim 1 wherein mild basic conditions are employed.
 3. The method of claim 2 wherein a 50% aqueous methyl amine is employed to provide said basic conditions.
 4. The method of claim 1 wherein a strong basic medium is employed.
 5. The method of claim 4 wherein 1M NaOH is employed as the strong basic medium.
 6. The method of claim 1 wherein room temperature or slight heating is employed. 